Or to put it more succinctly: Apple cannot retain the 30% if it was the cause of removal for an otherwise rules-abiding application. It's known as the doctrine of unclean hands (or possibly may even just be a plain ol' breach of contract).
Does anyone actually document Apple keeping 30%? It is my understanding that this is from a 3rd party interpretation of the contract and that Apple only retrieves the 70% they paid the developers.
If anyone takes this one to court, I'm sure Apple's legal team will try to paint that 30% they take as just a 'fee' to cover the infrastructure costs and that the infrastructure was still used to make the sale even when the customer is asking for a refund. (Not that I agree with what they are doing)